The objectives of Project 1 (Classification and Integration) are to (a) continue research evaluating classification and measurement issues that affect the identification of children as learning disabled (LD), with a focus on response to instruction (RTI) models; and (b) expand use of meta-analytic methods to integrate research across domains of LD, including reading comprehension and executive functions. Specific Aim 1 (Classification and Identification) addresses the nature and reliability of different methods for identifying children with LD based on simulated data and actual data from Projects 2-4. Simulations include (a) estimation of expected agreement when classification is made with multiple unreliable variables and various cut points; (b) identification of inadequate responders using different methods and cut points as well as other subgroups, such as so-called gifted LD or twice exceptional children; and (c) estimation of efficiency and utility in relation to different base rates and number of assessments. Similar comparisons will be made using actual data on intervention response from Project 3 (Intervention). Specific Aim 2 (External Validity of RTI Models) addresses the validity of the intervention response criteria evaluated under Aim 1. Using data collected under Projects 2 and 4, we will compare adequate and inadequate responders from Project 3 (Intervention) on cognitive assessments of executive functions and other domains. We will work with Project 4 (Neuroimaging) to compare adequate and inadequate responders on structural and functional neuroimaging measures. In addition, intervention response criteria will be compared to criteria generated by other proposed classifications, including IQ-discrepancy, low achievement, and cognitive strengths and weaknesses models. Specific Aim 3 (Integration) continues and expands our work on empirical synthesis from the previous five years. We propose to continue meta-analytic work addressing (a) predictors of intervention response; (b) executive functions in relation to different academic domains, especially reading comprehension and written expression; and (c) expand previous meta-analyses of intervention outcomes.